White space frequency bands are frequency bands allocated to television (TV) broadcasting service and to wireless microphone service, but not used in a local geographic area. Recent Federal Communication Commission (FCC) rules allow unlicensed access to white space frequency bands in the United States as long as such access does not interfere with TV and wireless microphone transmission (i.e., “incumbent” or “primary user” access to the frequency bands). Non-U.S. jurisdictions may also in the future implement similar provisions for access to television frequency bands. Available white space frequency bands may have variable bandwidths, and they may be non-contiguous and location-specific. These aspects make white space transmission networks different from conventional wireless transmission networks.
Conventional media access control and physical layer protocols may not support variable and non-contiguous frequency transmission as is typically needed in order to transmit over white space frequency bands. Conventional approaches to adapting a signal to an available spectrum include SampleWidth, SWIFT, and Jello. SampleWidth changes the bandwidth of a signal by adjusting the ticking rate of the baseband clock, which is equivalent to changing the signal's sampling rate. SWIFT and Jello split an orthogonal frequency-divisional signal into non-contiguous spectrum bands.